Apparatus for drying materials



April 2, 1946. MITTELMANN 2397,5 35

APPARATUS FOR DRYING MATERIALS Filed Nov. 5, 1941 Patented Apr. 2, 1946 UNITED STATES PATENT OFFICE APPARATUS FOR DRYING MATERIALS Eugen Mittelmann, Chicago, Ill.

Application November 3, 1941, Serial No. 417,585

2 Claims.

This invention relates to apparatus for the heating and drying of moisture-containing materials and particularly concerns the use of high frequency electrostatic fields in the drying of wooden members.

Wood having high moisture content must be treated in some manner to remove the greater part of the moisture in order to be utilized for most purposes. Kiln drying is one of the only commercially available methods used, but the apparatus required is expensive and cumbersome and the time necessary to remove so much of the moisture as necessary for producing wood with satisfactory commercial properties is of the order of days. By my new apparatus, which utilizes the heating effects of electrostatic fields, the time required to properly dry wooden members has been reduced to the order of minutes.

I am aware that attempts have heretofore been made to utilize the heating effects of electrostatic fields for the drying of wood and the like materials. Nevertheless, my invention contemplates means radically departing from said attempts and resulting in great improvements over accomplishments produced thereby.

The primary object of this invention is to provide a novel and improved means for heating wood or other materials utilizing electrostatic fields.

A further object of the invention is to provide a novel and improved means for heating wood or other materials whereby the heat produced will be evolved internally of the material being heated.

A further object of this invention is to provide a novel means for heating wood or other materials by means of electrostatic fields produced by a high frequency generator, whereby said generator will be operable at its highest efiiciency.

Another object of the invention is to provide a novel and improved means for heating wood or other materials by electrostatic fields whereby a maximum transfer of power to the material will be effected with a minimum danger of fiashover.

A still further object of this invention is to provide a novel and improved apparatus for heating wood or other materials by electrostatic fields whereby small electrodes may be utilized to heat large quantities of wood; only low voltages will exist across exposed portions of the apparatus; little or no radiation will occur due to positioning of the electrodes; the electrodes may form part of the oscillatory circuit of the high frequency generator.

With the foregoing and other objects in view,

which will appear as the description proceeds, the invention consists of certain novel features of construction, arrangement and combination of electrical and mechanical parts and elements, hereinafter fully described, symbolically illustrated in the accompanying drawing, and particularl pointed out in the appended claims, it being understood that various changes in the form, proportion, size and minor details, and arrangement of the various elements of the apparatus, may be made without departing from the spirit or sacrificing any of the advantages of the invention.

For the purpose of facilitating an understanding of my invention, I have illustrated in the accompanying drawings a preferred embodiment of the apparatus thereof and symbolic representations explanatory of the operational characteristics and principles involved, from an inspection and examination of which, when considered in connection with the following description and explanation, my invention, the mode of construction, assembly, operation and arrangement of elements of the apparatus thereof, and many of its advantages and features should be readily understood and appreciated.

Referring to the drawing in which the same characters of reference are employed to indicate the corresponding or similar parts throughout the several figures of the drawing:

Fig. 1 is a perspective view showing an arrangement of electrodes for heating a wooden member by utilizing electrostatic fields in accordance with my invention.

Fig. 2 is a schematic view of the arrangement shown in Fig. 1 showing the electrostatic flux lines.

Figs. 3 and 4 are views similar to those of Figs. 1 and 2, respectively, showing an arrangement utilizing paired electrodes.

Fig; 5 is a perspective view of an arrangement utilizing cylindrical electrodes and intended for the heating of a member having a circular cross section.

Fig. 6 is a schematic representation of an arrangement similar to that illustrated in Figs. 1 and 2, but utilizing a grounded electrode.

The relatively small electrodes of my new arr ngement each have a width substantially greater than its thickness and are dis osed in substantially the same plane spaced from the surface of the material being treated. The surface of the material is hence parallel to the voltage gradient vector v between the electrodes. This is also true of the planes of the electrodes,

time.

although in many cases the voltage gradient vector will be in the plane of the electrodes.

I have found that the flux, or electrostatic lines of force for such an arrangement assume a configuration wherein the greatest density of lines is in the center of the member heated, said density being substantially uniform for the distance between electrodes.

Such an arrangement is shown in its basic form in Figs. 1 and 2. The electrodes l4 and I5 are relatively narrow members of small area and are spaced a short distance above the surface of the member ID as shown and, accordingly, the path through the material is electrically shorter than the direct path between the electrodes. The electrodes are connected with a source of high frequency oscillations l3 and in my preferred embodiment are a part of the oscillating or frequency determining circuit. The flux F assumes subst ntially the pattern shown in Fig. 2.

The concentration of flux F centrally of member l0 causes the evolution of heat at the center of the member rather than at the surface. In effect, therefore, the member is heated from the center outwardly, rather than from the surfaces inwardly, as in all other previous methods. The drying is thus accomplished quicker since the moisture evaporates from the entire member simultaneously rather than from a portion at a In addition to this, hydrostatic pressure set up by evaporation in the interior of the member, by reason of evolution of heat from the center outwardly, forces the moisture out of the member. During the process, for example, the moisture will be seen actually dripping from the member. Because of this feature of forcing the moisture from the material, considerable energy otherwise necessary to cause evaporation of all the moisture is conserved.

The volume of material heated by means of my new apparatus and method in nowise depends upon the area of the condenser electrodes. In this way, the electrodes may be made quite small and the capacitance of the system kept down so that the electrodes may be part of an oscillating circuit. The constants of the circuit are chosen to assure resonance and high impedance, to match the high impedance of the generator feeding the oscillatory circuit. The electrodes may 'be spaced apart along the member In thereby increasing the ohmic resistance of the system, decreasing the capacitance, and in no way affecting voltage, since the air spaces'may be kept at a minimum. The adjustment of the physical disposition of electrodes aids in matching the circuit to the generator.

For a two-inch (2") wooden member, and a terminal voltage of about 9000, the voltages across the air spaces will be about 500 volts while the drop through the member is of the order of 8000. Since the system now has a substantial ohmic component. its antenna effect will be limited regardless of how far apart the electrodes are placed since this would greatly increase said ohmic component.

Various other arrangements for carrying out my invention are shown in Figs. 3 to 6. In Fig. 3 an increased power absorption, and hence faster heating, is obtained by disposing pairs of electrodes l6-ll, and l8l9, on opposite sides of the member 10 to produce a denser field of greater uniformity with respect to the faces I0.

. The flux F will assume substantially the pattern shown in Fig. 4. The pairs of electrodes iii-l1 and I 8l9 are each connected to the same lead so that each electrode is. at the same potential as its paired mate.

In Fig. 5 I have shown an arrangement whereby a cylindrical member 20 may be heated. A pair of cylindrical or circular electrodes 2| and 22 are arranged in the same cylindrical surface spaced above the member 20. will be substantially that of Fig. 4, but symmetrical with respect to the axis of the member 20. The voltage gradient vector v in this case is parallel to the cylindrical surface defined by the surfaces of the electrodes, and to the surface of the member 20.

In Fig. 6 I have shown a highly satisfactory arrangement whereby the total capacity of the system may be reduced quite substantially. The result is a closer and improved coupling. By means of the central grounded electrode 23, higher than ordinary voltages may be applied to the outer electrodes without danger of flashover.

Actual power absorption test measurements upon wooden members made by means of a high frequency wattmeter have shown that with the same high frequency voltages across the electrodes, ten to twenty times as much power is absorbed by using my invention than by using an arrangement wherein the wooden member is disposed between two large electrodes facing each other. The high efliciency of systems utilizing my invention enables the heating and drying to be accomplished in a few minutes. Consequently, my invention is applicable to the continuous drying of members moving along conveyors.

In the case of drying wood, for example, it should be appreciated that the drawing and description herein have covered the barest details and do not include reference to warpage control, humidity control, frequency control, or weight, moisture and temperature control. All of these factors, while not included in this description, are, nevertheless, to be considered in the commercial and practical application of my invention.

With regard to the material with which it is contemplated that my invention shall be used, almost any substance of a dielectric nature may be subjected to my apparatus and method. Such substances which require heat for drying, curing, or causing chemical changes to occur, may be advantageously treated. For example, rubber may be cured, ceramic materials may be dried, shatter-proof glass, plywood, and socalled wooden plastics may be bonded, and many other substances dehydrated quickly and efficiently by utilizing my invention.

It is believed that my invention, its mode of construction, arrangement, assembly, association of elements, and many of its advantages and features should be readily understood from the foregoing without further description, and it should also be manifest that while preferred embodiments of the invention have been shown and described for illustrative purposes, the details are, nevertheless, capable of wide variation within the purview of my invention.

What I claim and desire to secure by Letters Patent of the United States is:

1. In an electrostatic heating apparatus for heating members of dielectric material, a high frequency alternating current generator, a pair of condenser electrodes coupled to said generator, said electrodes being arranged parallel to a single surface of said material, and a third electrode, parallel to said surface of said material The flux effect and disposed between said pair of first mentioned electrodes, said last mentioned electrode being grounded.

2. In an electrostatic heating apparatus for heating members of dielectric material, a high frequency alternating current generator having a pair of opposite potential terminals, a pair of condenser electrodes coupled to said opposite potential terminals, each of said electrodes having a width substantially greater than its thickness, 10

said electrodes being arranged with their wider surfaces parallel to a single surface of said material, said electrodes being spaced longitudinally of the material to be heated, and a third, grounded electrode in non-overlapped relation to said pair of first mentioned electrodes and symmetrically positioned with respect to said first mentioned pair of electrodes.

EUGEN MI'I'I'ELMANN. 

